For example, brightness of an outside is measured by an illumination meter to control a target such that the luminance of a backlight on a liquid crystal screen is adjusted or streetlights are automatically turned on.
Such illumination meter is formed by a light receiving element that converts the intensity of received light (light intensity) into a current corresponding to the light intensity.
However, silicon (Si) that is a material of the light receiving element has a peak of sensitivity with respect to an infrared light, and hence two light receiving elements that are different in spectral characteristic so that a difference is generated in a predetermined wavelength region, for example, a visible light or an ultraviolet light and an output is cancelled in the other region are used in combination to obtain a desired spectral characteristic in order for a sensor to be sensitive to light in the predetermined wavelength region.
Thus, the light receiving elements different in spectral characteristic are appropriately combined together to detect the light with respect to the visible light, to thereby enable the spectral characteristic close to that of the naked eye, or to detect the ultraviolet light.
As a technology for obtaining the desired spectral characteristic by combining the two light receiving elements together as described above, there is proposed a “semiconductor photodetection device” disclosed in Patent Document 1.
Patent Document 1: JP 01-207640 A
In this technology, two n-type layers different in depth are formed on a p-type substrate to form two photodiodes different in spectral characteristic, and a difference in current between those photodiodes is taken to detect light in an ultraviolet region.
However, in the conventional technology, in order to increase an SN ratio to improve sensitivity, it is necessary to increase a current of the light receiving element. Therefore, the light receiving element itself is required to have a large size.
When the light receiving element becomes larger, there is a problem that it is difficult to reduce a sensor size because an IC chip on which the light receiving element is formed is also increased in size.